Traditionally, katana swords are not single bevel, but rather they have a characteristic geometry known as a "shinogi-zukuri" blade shape. Shinogi-zukuri refers to a type of blade construction where there is a distinct ridge line (shinogi) that runs along the sides of the blade, separating the flat portion called the shinogi-ji from the cutting edge.

The cutting edge of a katana is typically sharpened on one side, known as the "omote" side, while the other side, called the "ura," is flat or slightly concave. This creates a differential bevel known as a "hamon." The omote side of the blade is usually sharper, while the ura side contributes to the overall balance and strength of the sword.

This asymmetrical bevel is designed to optimize cutting performance by creating a sharper edge on one side while providing stability and strength on the other. It allows the blade to slice through targets with precision while reducing resistance and drag.

However, it's worth noting that there can be variations in blade geometry and bevel configurations across different types of Japanese swords and the work of different swordsmiths. Some specialty blades, such as those used for specific purposes or in certain regional styles, may have different bevel designs or be fully single bevel.

In summary, while traditional katana swords typically have an asymmetrical bevel with a sharp omote side and a flat or slightly concave ura side, there can be variations in blade geometry depending on the specific swordsmith, style, or purpose of the sword.